This invention relates to a balloon catheter used in percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA), in which constricted areas or obstructions such as in the coronary artery, limb arteries, the renal artery, or peripheral vessels are treated by dilation, and to a method for manufacturing this balloon catheter, and more particularly relates to a balloon catheter with improved characteristics for the catheter shaft distal end portion, including the balloon, and to a method for manufacturing this balloon catheter.
A balloon catheter is generally made up of a catheter shaft and a vascular dilation balloon provided to the distal end portion of this catheter shaft. Angioplasty using a balloon catheter such as this is conducted by the following procedure. First, a guide wire is passed through the afflicted site (such as an obstruction), the balloon catheter is inserted along this guide wire until the balloon is at the afflicted site, and the balloon is inflated by supplying a suitably diluted contrast medium or the like to an inflation lumen. After this inflation, the balloon is depressurized and deflated, and the balloon catheter is taken out of the body.
A specific example of a conventional balloon catheter, and the problems encountered with it, will now be described.
FIG. 5 illustrates the cross sectional structure of a conventional balloon catheter at its distal end portion. In the figure, 80 is a catheter shaft, 81 is an inner tube, 82 is an outer tube, 83 is a balloon, and 84 is an X-ray impermeable marker. The proximal end 85 of the balloon 83 provided at the distal end portion of the catheter shaft 80 is joined to the distal end portion of the outer tube 82, and the distal end 86 of the balloon 83 is joined in the proximity of the distal end portion of the inner tube 81. When this balloon 83 is depressurized and deflated, it wraps up as shown in FIG. 6. The following problems were encountered when a balloon catheter with a structure such as this was used at an afflicted site with a high degree of difficulty. When the surgeon applied force to the proximal end of the balloon catheter so as to align the balloon at a highly constricted site, the thin-walled balloon 83 deformed like a bellows (called xe2x80x9caccordioningxe2x80x9d), so the force applied to the proximal end was not sufficiently transmitted to the distal end, making it much more difficult for the catheter to pass through the afflicted site, and the balloon could not be accurately aligned with the constricted area. The cause of this was that the outer tube 82 and inner tube 81 were fixed to branched hubs, or the like, at the proximal end of the catheter, and were therefore securely restrained, and were weakly linked via just the thin-walled balloon 83 at the distal end portion, so the middle part between the distal end and proximal end portions was not restrained at all.
Balloon catheters with the structure illustrated in FIG. 7 have been proposed in an effort to solve this problem (see, for example, Japanese Laid-Open Patent Applications H3-51059, H4-2363, and H5-137793). In the figure, 90 is a catheter shaft, 91 is an inner tube, 92 is an outer tube, 93 is a balloon, and 94 is an X-ray impermeable marker. Specifically, since the inner tube 91 was joined to the inner wall surface of the outer tube 92 in the proximity of the distal end portion of the outer tube 92, and the outer tube 92 and the inner tube 91 were securely restrained by this joint 95, the balloon 93 did not accordion even at difficult afflicted sites with severe constriction, and the pushing force applied by the surgeon was transmitted to the distal end portion. Nevertheless, the following problems were encountered with these balloon catheters.
In the positioning and inflation of the balloon at the afflicted site, the balloon extends radially and longitudinally due to the pressure applied by a pressurizing fluid, but the inner tube inside the balloon, that is, the inner tube located between the distal end portion proximity of the outer tube and the distal end portion proximity of the balloon, is stretched along with the longitudinal extension of the balloon. Then, when the dilation of the afflicted site is completed and the balloon is deflated, the balloon 93 returns to its original dimensions because it is made from a pressure-resistant type of material, but as shown in FIG. 8, the stretched inner tube 91 does not return to its original length, and instead slackens. The reason for this is that because the inner tube is usually made from a material selected for its ability to slide smoothly over the guide wire, it does not exhibit the elastic changes that the balloon does, and is instead prone to plastic deformation and is easily stretched. In this state, the position of the inner tube is shifted with respect to the folding creases in the balloon, and this makes it much more difficult to rewrap the balloon when it is deflated, resulting in winging, and if another attempt is made to pass the catheter through the constriction, the wings often snag and prevent the catheter from passing through. Specifically, once the balloon has been inflated, it passes through the afflicted site with more difficulty the second and subsequent times. This situation is illustrated in FIGS. 9 and 10. FIG. 9(a) shows the state when the wings of the balloon 93 are wrapped in opposite directions around the inner tube 91, and FIG. 9(b) shows the state in which the wings 93a and 93b are not wrapped sufficiently and stick out. FIG. 10(a) shows the state when the wings of the balloon 93 are wrapped in the same direction around the inner tube 91, and FIG. 10(b) shows the state in which the wings 93a and 93b are not wrapped sufficiently and stick out.
A problem that is common to both of the balloon catheters shown in FIGS. 5 and 7 is that since the rigidity varies greatly in the outer tube distal end portion, this portion is prone to breakage when the balloon catheter is handled or when the guide wire is replaced. This is because the only things beyond the outer tube distal end portion are the slender inner tube and the thin-walled balloon, so discontinuity in the rigidity occurs.
Problems related to the very farthest point at the distal end portion of a conventional balloon catheter will now be described through reference to FIGS. 21 to 26. FIG. 21 is an enlarged cross section illustrating the very farthest point at the distal end portion of a balloon catheter. In the figure, 100 is a balloon and 101 is an inner tube. The inner tube 101 goes through and sticks out from the distal end portion of the balloon 100, and is bonded to the distal end-side bonded portion of this balloon by an adhesive agent layer 103. The distal end portion of the inner tube 101 retains the tubular shape of the inner tube, and has an edge 104 at the most distal end portion. A problem with this edge 104, however, was that it would snag when passing through the afflicted site in a blood vessel or through a curved section, making it difficult to pass the catheter through these areas.
In view of this, prior art has been proposed in which just the edge portion of the most distal end of the inner tube is removed, but at afflicted sites with a high degree of constriction, for instance, the difficulty of passing through the afflicted site or through curved sections has not been solved to satisfaction. Prior art in which the distal end tip of the balloon catheter is made flexible in order to improve this passage has been proposed in Japanese Laid-Open Patent Applications H2-271873 and H5-253304. Both of these disclose a structure in which the sleeve portion 111 (121) of the distal end portion of a balloon 110 (120) sticks out from an inner tube 112 (122) that forms a guide wire lumen (see FIGS. 22 and 23, which are simplified cross sections of the distal end tip). Here, in the example shown in FIG. 22, the outside diameter of the sleeve portion 111 formed integrally with the balloon 110 is reduced in steps toward the distal end, and in the example shown in FIG. 23, the outside diameter of the sleeve portion 121 is reduced to a pointed taper shape toward the distal end. In recent years, however, it has become necessary for a balloon to have better pressure-resistance strength, which has created the need to fabricate the balloon from a relatively hard material that stretches less. As a result, the distal end tip formed in this sleeve portion needs to have high rigidity.
Furthermore, the distal end tip needs to be slender in order to facilitate its passage. Prior art to this end includes the balloon catheter with a constricted most distal end portion at the distal end tip disclosed in International Laid-Open Patent Application WO88/6465, in which the sleeve of the balloon distal end portion is fused to the tube (inner tube) that forms the guide wire lumen, forming two layers of tube and sleeve, after which these two layers are chamfered.
The above-mentioned Japanese Laid-Open Patent Application H2-271873 discloses a structure in which the sleeve portion of the distal end portion of the balloon sticks out from the inner tube distal end portion, and the sleeve portion of the balloon forms the most distal end portion of the catheter. The effect of this is stated to be that the distal end tip is more flexible because the fixed surface area is increased and the fixing distance between the inner tube and the sleeve of the balloon distal end portion is shortened, and that the balloon distal end portion can be prevented from peeling away at the fixed portion between the inner tube and the sleeve of the balloon distal end portion during catheter insertion because this fixed portion is not exposed on the outer surface of the catheter. More recently, however, it has become necessary for the distal end tip to be both flexible and smaller in diameter, and while it was possible to achieve flexibility by increasing the fixed surface area and reducing the fixing distance between the inner tube and the sleeve of the balloon distal end portion, constricting or tapering the two-layer portion comprising the tube and sleeve was difficult due to the structure, and there seemed to be an insurmountable limit to how much the two-layer portion could be reduced in diameter. Also, there was an abrupt step where the two layers changed to a single layer, and this posed a serious obstacle to curving the balloon catheter distal end portion and passing it through afflicted sites with a high degree of constriction.
Also, the medical profession is now demanding catheters that will pass easily through afflicted sites with a high degree of difficulty, afflicted sites with a high degree of curvature, and portions with high surface resistance, such as through a stent.
To meet this demand, a catheter will have to be even slimmer and more flexible. Specifically, a balloon catheter needs to be slender enough that it can just squeeze through the gap through which the guide wire passes, and to be able to closely follow the guide wire as it enters acutely curved afflicted sites (see FIGS. 24 and 25). In FIGS. 24 and 25, 130 is a balloon, 131 is a sleeve on the far side of the balloon 130, 132 is a distal end tip, 132a is the distal end portion of the distal end tip, 133 is a guide wire, 140 is a blood vessel, 140a is a constriction, and 140b is a branched blood vessel branching off from the blood vessel 140. If the catheter is not able to follow the guide wire adequately into afflicted sites with a large degree of curvature or branched afflicted sites with sharp angles, then the guide wire may break while the balloon catheter is advancing. Also, a stent 141 has often been used in recent years to maintain the diameter of a blood vessel dilated with a balloon catheter (see FIG. 26). In the event of reconstriction within this stent, or reconstriction near the distal end portions where the stent is left, a balloon catheter has to be moved into the stent once again, but the distal end tip 132 may run into the coiled portion (strut) of the stent 141 and be unable to proceed any further, among other problems that are encountered.
Problems related to the joining of a conventional catheter shaft and balloon will now be described through reference to FIGS. 27 and 28. Means such as heat fusion and adhesive bonding have been used in the past to join a catheter shaft and a balloon, and various methods have been provided. For instance, Japanese Laid-Open Patent Application S61-92677 (Medical Tube with Attached Balloon) discloses a technique related to adhesive bonding, in which a tube and a balloon made of different materials are bonded with an adhesive agent composed of an addition polymerization type of silicone composition. All that is discussed here is that different materials can be bonded, and no mention is made about the properties of the adhesive agent, and particularly its hardness, after it cures. If the hardness of the adhesive agent portion is far higher than that of the catheter shaft or balloon, the rigidity will be discontinuous for the catheter as a whole, and when the balloon catheter is passed through a curved section within a blood vessel, it will be difficult for the balloon catheter to conform to the curved blood vessel, as shown schematically in FIGS. 27 and 28. In FIGS. 27 and 28, 150 is a catheter shaft to which a balloon 151 has been bonded with an adhesive agent of high hardness, 152 is a guide wire, 153a is a curved section of a coronary artery, for example, and 153b is a constriction.
In this case, the surgeon does not merely feel resistance as the balloon catheter is moved forward, and this is actually extremely dangerous, as there is the possibility that kinks 154a and 154b in the catheter could injure the blood vessel at the portion of discontinuous rigidity. Also, if the adhesive agent is very hard after curing, then the distal end tip will also be hard, making it extremely difficult to insert the catheter into the constriction 153b. 
Meanwhile, when heat fusion is used, it is not effective for all combinations of catheter shaft and balloon materials, and is therefore limited to combinations with which the miscibility of the resins is good when they are heat-fused. Therefore, this method is generally employed when the catheter shaft and balloon are made of the same material, and does not lend itself well to the joining of a catheter shaft and balloon made of different materials. Even when a catheter shaft and balloon made of different materials with good miscibility are heat-fused, the fused portion often becomes harder than the catheter shaft, which results in discontinuity in the rigidity of the catheter shaft and, at the same time, inevitably leads to a loss of flexibility in the distal end tip.
A conventional balloon, and the problems encountered with conventional balloons, will now be described. In general, a balloon must be strong enough not to burst when pressure is applied to the balloon, and must be such that the inflation can be safely controlled to the desired size, among other requirements. Also, the properties must be such that if the balloon should burst inside a blood vessel, it will be a tearing burst in the axial direction, which poses relatively little danger, rather than a pinhole burst that could damage the blood vessel or a tearing burst in the radial direction, which makes the balloon more difficult to remove from the blood vessel after bursting. It is also desirable for the walls of the balloon to be as thin as possible and for the balloon to have a small coefficient of friction so that it can pass through extremely constricted sections with ease. Also, it is important for the balloon to be made of a material with which no wings will be produced when the balloon is rewrapped as discussed above. Other requirements include the ability of the balloon to conform to and easily bend in curved sections of a blood vessel.
Materials that have been used in or proposed for conventional balloons include polyethylene terephthalate, polyethylene, polyvinyl acetate, ionomers, polyvinyl chloride, polyamide, polyamide-based thermoplastic elastomers, polyester-based thermoplastic elastomers, and polyurethane-based thermoplastic elastomers.
Because of its strength, a polyethylene terephthalate (PET) material can be molded into a thin-film pressure-resistant balloon, and is a typical material having low expansion characteristics, as disclosed in Japanese Laid-Open Patent Application S63-26655 and Japanese Patent Publication H3-37941. A balloon composed of PET, however, lacks flexibility at room temperature and near body temperature because its glass transition point is over 60xc2x0 C., and thus inflation takes a long time, and when the balloon is inflated at a high pressure, there is a serious danger of injuring the afflicted site. This material is also difficult to wrap and is prone to the above-mentioned winging, so it tends to scratch blood vessels. Furthermore, because the glass transition point is so high, and the balloon is in an excessively crystalline state at room temperature or near body temperature, the balloon is susceptible to wrinkling, and pinhole bursting tends to occur at these wrinkles.
A balloon formed from polyethylene, polyvinyl acetate, an ionomer, polyvinyl chloride, or a copolymer or mixture of these has relatively low material strength, so only low pressure resistance can be obtained. Thus, to achieve the required inflation pressure resistance, the walls of the balloon have to be made thicker. Wrapping is facilitated by making the walls thicker, but the drawback is that the wrapped balloon has a larger diameter and is bulkier.
A balloon formed from a polyamide material has high pressure resistance comparable to that of a PET material, and also has some flexibility, so the problems encountered with PET, namely, winging during wrapping and susceptibility to pinhole bursting, are ameliorated to a certain extent. Because of the high tensile strength of a polyamide material, however, the walls of the balloon are made thinner, and consequently shape retention is poor in the wrapping of the balloon, and winging tends to occur during rewrapping. Also, a polyamide material has a relatively large coefficient of friction and is highly hygroscopic, so inside a blood vessel, which is a particularly humid environment, a problem is the large amount of friction with the vascular walls. Methods for manufacturing a balloon using a polyamide material are discussed in Japanese Laid-Open Patent Applications H3-57462 and H3-57463. These manufacturing methods entail numerous steps, including a heat fixing step, in addition to the process being complicated and difficult to control, so drawing unevenness tends to occur in the balloon, and circumferential tear bursting may occur during the use of the balloon, so there is the danger of damaging the blood vessels.
A balloon composed of a polyurethane, polyamide-based thermoplastic elastomer, polyester-based thermoplastic elastomer, or other such block copolymer is excellent because it is sufficiently strong and is flexible, but because it is softer than a polyamide, its shape retention in wrapping is poor. Therefore, a heat treatment must be performed to impart shape retention, but this heat treatment is difficult, the balloon diameter shrinks severely when exposed to an elevated temperature during sterilization, and it is extremely difficult to control the final balloon diameter. Also, polyamide-based thermoplastic elastomers are often used to modify polyamide resins, and polyester-based thermoplastic elastomer are used to modify polyester resins, but polyamide-based thermoplastic elastomers and polyester-based thermoplastic elastomers generally have a high modulus elasticity and are not readily modified in terms of increasing flexibility, and their miscibility with other resins is also poor. Thus, a drawback to these materials is that they can only be used in applications limited to the above-mentioned combinations.
Various balloon materials were described above, but none of these balloon materials could satisfy the expansion characteristics required of a balloon. This is because the desired expansion characteristics of a balloon for an afflicted site are not constant. Specifically, a balloon must be inflated under a relatively high pressure for afflicted sites such as those where severe calcification has occurred, so the balloon must be able to withstand this inflation pressure, and it is preferable for the balloon to have low expandability, wherein changes in balloon diameter are relatively small with respect to changes in inflation pressure. On the other hand, in the case of a large afflicted site, it is preferable for the balloon to have high expandability, so that its size when inflated can match the size of the afflicted site.
Because of the difficulty of fabricating a balloon having the characteristics of both low and high expandability using a single type of material, the balloon must be made from a combination of two or more types of material, but this is extremely disadvantageous for industrial purposes because of the higher costs involved, etc. To fabricate a balloon with high expandability, a material with relatively low strength must be selected, and as a result, the walls of the balloon inevitably have to be made thicker to achieve pressure resistance, and because this makes the balloon diameter larger when wrapped, the balloon catheter does not pass through narrow sections well. From the standpoint of enhancing shape retention when the balloon is wrapped, it is advantageous for the balloon walls to be thinner, but then the strength is inadequate. Meanwhile, if a high-strength material is used and the balloon walls are made thin, the balloon will have little flexibility during wrapping, and it will not adequately fulfill its function as a balloon catheter. There has been a need for a balloon material that would have a good balance between these two conflicting characteristics.
In light of the above problems, the following (1) to (4) are objects of the present invention.
(1) To provide a balloon catheter that solves all of the problems regarding ease of use encountered in the past. Specifically, to provide a balloon catheter that solves these problems by preventing the inner tube from slackening after balloon inflation and thereby improving the rewrapping of the balloon, preventing breakage through a reduction in the discontinuity of the rigidity of the joined portions of the outer tube and the balloon, adjusting the hardness of the shaft of the balloon portion so as to improve passage through afflicted sites with severe constriction and through curved blood vessels, and preventing xe2x80x9caccordioningxe2x80x9d so as to enhance the transmission of the pushing force.
(2) To make the distal end tip of the balloon catheter more flexible and slender, and markedly improve conformability to the guide wire and passage through constrictions.
(3) To provide a balloon catheter that not only has sufficient strength after the catheter shaft and balloon have been joined and integrated as compared to a conventional method for joining a catheter shaft and balloon, but also has no discontinuity in the catheter shaft rigidity related to the hardness of the bonded portion, is able to conform easily to curved blood vessels, and has a distal end tip that remains flexible after the curing of the adhesive agent.
(4) To provide a balloon catheter equipped with a balloon that has excellent flexibility and pressure resistance, is easily wrapped, retains its shape when wrapped, and is easily rewrapped after being inflated.
To achieve the stated objects, the balloon catheter of the present invention is a balloon catheter having a catheter shaft with a double-tube structure comprising an outer tube and an inner tube through which a guide wire is passed, located at least in the proximity of the distal end portion of the catheter, a inflation lumen through which a pressure fluid is passed being provided between the inner tube and the outer tube, and a balloon disposed at the distal end portion of the catheter shaft and capable of being inflated, deflated, and wrapped by the pressure fluid, wherein the end of the balloon on the proximal side is joined in the proximity of the distal end portion of the inner tube, and a guide tube having an outside diameter smaller than the inside diameter of the outer tube and having an inside diameter larger than the outside diameter of the inner tube is disposed so as to form a double-tube with the outer tube, and the inner tube is not fixed, but passes through the interior of the guide tube in the axial direction.
With this structure, even though the inner tube is stretched when the balloon is inflated, the inner tube is able to slide through the guide tube in the axial direction, so the stretching is within the range of elastic deformation, and the inner tube returns to its original state when the balloon is deflated. Also, the rigidity of the joined portions of the outer tube and balloon is continuous, preventing any breakage in these portions.
It is preferable here for the guide tube to be joined in a state of being offset to the inner wall surface of the outer tube. This makes it possible for the walls to be thinner in the joined portion of the guide tube with respect to the outer tube, and ensures a good flow of the balloon inflation pressurized fluid that flows through the inflation lumen between the outer tube and inner tube.
By having the distal end of the guide tube butted up against the proximal end side of an X-ray impermeable marker joined to the inner tube, or having the distal end of the guide tube butted up against the joint of the balloon where it is joined to the inner tube, the pushing force applied from the proximal side of the outer tube of the catheter shaft will be more readily transmitted to the distal end portion of the inner tube via the guide tube.
By making the guide tube walls thinner toward the distal end, the hardness of the shaft of the balloon portion can be adjusted so that it continuously becomes softer nearer to the distal end.
When the distal end of the guide tube is butted up against the joint between the inner tube and the balloon distal end, an X-ray impermeable marker is provided over the outer surface of the guide tube.
It is preferable for the guide tube to be composed of a polyimide, or to be composed of one or more members of the group consisting of polyamide elastomers, polyester elastomers, polyurethane elastomers, and polyolefin elastomers.
Here, if a spring-like coil is embedded in the guide tube, this coil will increase the rigidity of the guide tube with respect to the transmitted pushing force, and the hardness can be suitably adjusted with respect to curvature. In this case, the spring-like coil is preferably composed of an X-ray impermeable material.
It is also preferable if the inner tube protrudes from the balloon distal end portion, and a distal end tip formed at the junction with the distal end portion has a pointed taper shape, and the wall thickness of the distal end taper portion decreases continuously in the distal end tip from the proximity of the most distal end of the distal end-side balloon joint up to the most distal end of the catheter, the average thickness reduction gradient is 6 to 60 xcexcm/mm, the length from the most distal end of the distal end-side balloon joint to the most distal end of the catheter is 3 to 10 mm, and the tube wall thickness at the most distal end of the distal end taper portion is 10 to 50 xcexcm.
It is even more favorable here if the average thickness reduction gradient of the distal end taper portion is 10 to 30 xcexcm/mm, the length from the most distal end of the distal end-side balloon joint to the most distal end of the catheter is 4 to 7 mm, and the tube wall thickness at the most distal end of the distal end taper portion is 20 to 40 xcexcm.
If the average thickness reduction gradient of the distal end taper portion exceeds 60 xcexcm/mm, the distal end portion from the distal end to the proximal side will suddenly become hard, making it difficult for the distal end tip to conform to the guide wire. On the other hand, if this average thickness reduction gradient is less than 6 xcexcm/mm, the wall thickness of the taper portion most distal end portion will increase and hinder catheter passage, or the distal end tip will be too long and the frictional resistance will be great as the catheter passes through the afflicted site. It is therefore preferable for the average thickness reduction gradient to be adjusted to 6 to 60 xcexcm/mm. A setting of 10 to 30 xcexcm/mm is even better.
As to the length of the distal end tip from the most distal end of the distal end-side balloon joint to the catheter most distal end, if the length of the distal end tip is less than 3 mm, then even if the average thickness reduction gradient is between 6 and 60 xcexcm/mm, sufficient flexibility and a reduction in diameter at the distal end portion will not be achieved. On the other hand, if the length of the distal end exceeds 10 mm, a large force will be required to overcome the frictional resistance produced by the distal end tip and to pass through the afflicted site, the walls will be too thin in the distal end portion, and the distal end portion will be susceptible to being broken by the pushing force of the surgeon.
Furthermore, even if the average thickness reduction gradient is 6 to 60 xcexcm/mm and the length of the distal end tip is between 3 and 10 mm, it is undesirable for the tube walls of the distal end taper portion most distal end to be either too thin or too thick, and it is preferable for the wall thickness of the most distal end to be set within a range of 10 to 50 xcexcm while the above conditions are also met. If the tube wall thickness of the distal end tip most distal end is less than 10 xcexcm, the distal end portion will be too soft and will stick to the guide wire, so the frictional resistance will be greater during pushing, resulting in the undesirable occurrence of xe2x80x9caccordionxe2x80x9d deformation. If the wall thickness is over 50 xcexcm, though, the distal end tip will not be sufficiently flexible and no reduction in the diameter of the distal end portion will be obtained.
It is even more favorable to form an adhesive agent layer at the stepped portion produced between the inner tube and the most distal end of the distal end-side balloon joint so as to eliminate this step, decreasing the discontinuity in rigidity and the step in the proximity of the balloon catheter distal end portion. The step and the discontinuity in rigidity may also be decreased by forming the most distal end of the sleeve portion of the distal end-side balloon joint in a taper so as to eliminate the step.
Furthermore, it is preferable for the most distal end of the distal end taper portion to be chamfered, and for the inner tube to be composed of HDPE (High-Density PolyEthylene) or a fluororesin such as polytetrafluoroethylene.
The method for manufacturing a balloon catheter equipped with the above-mentioned distal end tip includes a step in which the portion of the inner tube forming the distal end taper portion is locally heated, a tensile force is applied to both ends of the portion to stretch it to a specific length, thereby constricting the inner tube, and this constricted portion is cut to a specific length, and the inner tube having the distal end taper portion is inserted into an outer tube, and the inner tube and the balloon distal end portion are joined so that the distal end taper portion protrudes from the balloon distal end portion, thereby forming the distal end tip.
The second method for manufacturing a balloon catheter equipped with the above-mentioned distal end tip includes a step in which the sleeve portion of a distal end-side balloon joint is joined to the inner tube, after which the most distal end of the sleeve portion is locally heated, a tensile force is applied to the balloon distal end portion and the heated inner tube on the distal end side to stretch it to a specific length, thereby constricting the inner tube and the most distal end in the sleeve portion, and this constricted portion is cut to a specific length, and the inner tube having the distal end taper portion is inserted into an outer tube, and the inner tube and the balloon distal end portion are joined so that the distal end taper portion protrudes from the balloon distal end portion, thereby forming the distal end tip.
The above-mentioned diameter reduction in the distal end tip and making it more flexible may be accomplished by working the inner tube that forms the guide wire lumen ahead of time and then assembling the balloon and other parts, or the distal end portion of an assembled balloon catheter may be worked. Reducing the diameter by working while the parts are not yet assembled is preferable from the standpoint of boosting assembly efficiency.
The distal end tip can be easily worked by locally heating part of the inner tube forming the guide wire lumen, and stretching to a specific length. In this case, it is preferable to form the distal end taper portion in a state in which a mandrel has been inserted into the inner tube that forms the guide wire lumen. As a different working method, an excimer laser may be used to achieve the desired wall thickness reduction gradient. Working takes longer with this method, but the wall thickness can be adjusted more accurately.
The easiest working method is abrasion with a file. This method, however, produces filings of the material, which is not suited to working in a clean room, and requires a washing step after the working.
As to the adhesive agent used to join the proximal end of the balloon in the proximity of the distal end portion of the outer tube and to join the distal end of the balloon in the proximity of the distal end portion of the inner tube, the durometer hardness (D value) when the adhesive agent is cured is preferably at least D16 and no more than D70.
Here, the adhesive agent is preferably either a two-liquid normal temperature (room temperature) curing type of adhesive agent, a UV-curing adhesive agent, or a water-absorption curing type of adhesive agent. It is even more favorable for the two-liquid normal temperature (room temperature) curing type of adhesive agent to be a urethane type, silicone type, or epoxy type, and also more favorable for the water-absorption curing type of adhesive agent to be a cyanoacrylate type of urethane type.
It is particularly preferable for the balloon pertaining to the present invention to be composed of a polymer alloy material including a styrene-based thermoplastic elastomer as a constituent component. It is preferable for the polymer alloy material to include one or more members of the group consisting of polyester resins, polyester-based thermoplastic elastomers, polyamide resins, polyamide-based thermoplastic elastomers, polyurethanes, and polyphenylene ethers as constituent components.
It is even better for the polymer alloy material to include a polyolefin as a constituent component.
It is favorable if the styrene-based thermoplastic elastomer is contained in an amount of 1 to 30 wt %, and if this styrene-based thermoplastic elastomer is a type that imparts functional groups. It is also favorable for the styrene-based thermoplastic elastomer to be a hydrogenation type.
If a styrene-based thermoplastic elastomer with good resin modification properties and excellent miscibility is thus used as one of the constituent components of the polymer blend in the balloon material pertaining to the present invention, the properties of the balloon thus formed, and particularly its flexibility, wrapability, wrapped shape retention, assembly workability, and so on, will be improved, and a wide range of control over expandability will be achieved, making it possible to provide a balloon that is thin-walled and pressure-resistant while having particularly high expandability. With this balloon material, materials that were immiscible in the past are miscibilized, and it is possible to combine a plurality of resins having favorable properties for a balloon, and as a result, a superior balloon in which the weak points of existing materials are compensated can be provided.